Older people usually present with adverse drug events (ADEs) with nonspecific symptoms such as cognitive decline, recurrent falls, reduced mobility, and/or major deterioration. The aims of this study were to assess the ADEs of patients with dementia and presenting neuropsychiatric/behavioral, and psychological symptoms in dementia (BPSD) and to categorize and identify the principal factors that allow to prevent ADEs, and separately ADEs that result in falls. To that end, a one-year prospective study in a psychogeriatric ward (July 2015 to July 2016) was performed. All patients admitted to this ward were eligible for enrolment. Patients who met any of the following criteria were excluded from the study: Patients without cognitive impairment, a length of stay under 7 days, and palliative or previous psychiatric pathology. We included 65 patients (60% women, 84.9 years ± 6.7) with mild to moderate cognitive impairment, moderate to severe functional dependence, and a high prevalence of geriatric syndromes and comorbidity. A total of 87.7% were taking five or more drugs (mean 9.0 ± 3.1). ADEs were identified during the interdisciplinary meeting and the follow up by clinical record. Sixty-eight ADEs (81.5% patients) were identified, of which 73.5% were not related to falls. From these, 80% were related to drugs of the nervous system. The Naranjo algorithm determined that 90% of ADEs were probable. The severity of the ADEs was Category E in 34 patients (68%). The number of preventable ADE according to the Schumork–Thornton test was 58%. The main ADE was drowsiness/somnolence (27.7%). ADEs related to falls represented a 26.5%. The balance between effective treatment and safety is complex in these patients. A medication review in interdisciplinary teams is an essential component to optimize safety prevention.